This invention relates to a centraliser for a prosthetic implant, in particular a prosthetic femoral stem for implantation in a patient's femur for hip replacement surgery.
Centralisers or spacers are provided for fitting to the distal end of a femoral hip replacement stem in order to keep the implant stem away from the internal surface of the cavity of the bone in which the stem is to be inserted. In the case of stems which are cemented in the bone cavity, there is a space between the stem and the internal surface of the cavity of the bone in which bone cement is placed. Controlling the position of the stem within the surrounding bone cement mantle is vital to the long-term survivability of the replacement joint. Cement can be deposited in the bone cavity and the stem with the attached centraliser is then inserted. It is important to try to obtain an even and intact cement mantle around the stem.
Known centralisers are in the form of caps which fit over the distal end of the stem and centralisers which are fixed inside the drilled end of a stem. Centralisers are also known, for example as described in U.S. Pat. No. 4,658,351, which are of ring form which can have a tapered inner surface corresponding to the tapered surface of the distal end of the femoral stem on which the centraliser is located.
U.S. Pat. No. 3,793,650 describes a centraliser or spacer which has spring members which extend from the stem for contact with the wall of the bone cavity.
European patent No. EP0427444B describes a centraliser or spacer in the form of a cap for insertion on the end of a hip stem with fins or wings extending outwardly from the cap which are adapted to fold circumferentially and inwardly towards the body portion of the cap.